The present disclosure relates generally to switching devices, and more particularly to operation and configuration of the switching devices.
Switching devices are generally used throughout industrial, commercial, material handling, process and manufacturing settings, to mention only a few. As used herein, “switching device” is generally intended to describe any electromechanical switching device, such as mechanical switching devices (e.g., a contactor, a relay, air break devices, and controlled atmosphere devices) or solid state devices (e.g., a silicon-controlled rectifier (SCR)). More specifically, switching devices generally open to disconnect electric power from a load and close to connect electric power to the load. For example, switching devices may connect and disconnect three-phase electric power to an electric motor. As the switching devices open or close, electric power may be discharged as an electric arc and/or cause current oscillations to be supplied to the load, which may result in torque oscillations. To facilitate reducing likelihood and/or magnitude of such effects, the switching devices may be opened and/or closed at specific points on the electric power waveform. Such carefully timed switching is sometimes referred to as “point on wave” or “POW” switching. However, the opening and closing of the switching devices are generally non-instantaneous. For example, there may be a slight delay between when the make instruction is given and when the switching device actually makes (i.e., closes). Similarly, there may be a slight delay between when break instruction is given and when the switching device actually breaks (i.e., opens).
Accordingly, to facilitate making or breaking at a specific point on the electric power waveform, it would be beneficial to determine the delay. More specifically, this may include determining when the switching device makes or breaks.
Additionally, since the switching devices may make to supply electric power to a load, it would be beneficial to determine if there are any faults, such as a phase-to-ground short or a phase-to-phase short, before fully connecting electric power to the load. For example, testing for faults before fully connecting electric power may enable the faults to be detected while minimizing the peak current and/or let through energy resulting from the fault condition.
Furthermore, switching devices may be utilized to provide electric power to electric motors. For example, in some applications, the switching devices may be included in a wye-delta starter or some other motor controlling device. As used herein, a “wye-delta starter” is intended to describe a device that controls operation (e.g., speed, torque, and/or power consumption) of an electric motor by connecting winding in the electric motor in a wye configuration, a delta configuration, or a mixed wye-delta configuration. In fact, in addition to controlling starting of the electric motor, the wye-delta starter may control operation and even stopping of the electric motor.
More specifically, the electric motor may be started by connecting the windings in the motor in a wye configuration to reduce voltage supplied to the windings, which may also reduce the torque produced by the motor. Once started, the windings in the motor may be connected in a delta configuration to increase the voltage supplied to the windings, which may increase the torque produced by the motor. However, as described above, opening and closing the switching devices to connect the electric motor in the wye configuration and to transition from the wye configuration to the delta configuration may discharge electric power (e.g., arcing) and/or cause current oscillations to be supplied to the motor. In some embodiments, reducing the likelihood and magnitude of electric arcing and/or current oscillations may increase the lifespan of the switching devices.
Accordingly, it would be beneficial to reduce the likelihood and magnitude of electric arcing and/or currently oscillations produced when making or breaking a switching device. More specifically, this may include opening and/or closing switching devices in the wye-delta starter at specific points on the electric power waveform.
Moreover, wye-delta starters generally supply electric power to electric motors to run the motors in wye or delta configuration. More specifically, when the motor is run in a wye configuration, the electric motor may use less electric power and produce a first (e.g., lower) torque level, and when the motor is run in a delta configuration, the electric motor may use more electric power and produce a second (e.g., higher) torque level. In other words, running the electric motor with a wye-delta starter enables two operating modes (e.g., less power consumption lower torque and more power consumption higher torque). However, there may be instances when it is desirable to operate the motor somewhere between the two operating modes. For example, it may be desirable to produce more torque than produced when operating in the wye configuration, but consume less electric power than consumed when operating in the delta configuration. Accordingly, it would be beneficial to increase the operational flexibility of a wye-delta starter.
After the electric motor is spinning, electric power may be disconnected from the motor for various reasons, such as a brownout or a lightning strike. More specifically, switching devices (e.g., contactors) may open to disconnect electric power. Once power is disconnected, the momentum of the rotation may keep the motor spinning, but friction (e.g., air resistance) may begin to slow the motor. As such, the frequency of the motor gradually decreases. Subsequently, the electric motor may be restarted by re-closing the switching devices to connect electric power to the motor. In some embodiments, such as reliability sensitive implementation, it may be desirable to restart the electric motor as soon as possible, for example, while the electric motor is still spinning. However, since the frequency of the motor is changing, the phase relationship of the motor relative to the electric power source is also changing, thereby creating a “beat” condition. Therefore, the motor may be out of phase from the source when re-closing the switching devices to reconnect electric power to the motor, which may result in current oscillations and/or torque oscillations. In some embodiments, minimizing the likelihood and magnitude of current oscillations and/or torque oscillations may increase the lifespan of the electric motor and/or a connected load. In some embodiments, minimizing peaks in the current may reduces nuisance tripping of protective circuitry (e.g., circuit breaker or fuses) and, thus, enable the protective circuitry to be sized more advantageously.
Accordingly, it would be beneficial to minimize the magnitude and likelihood of current oscillations and/or torque oscillations produced when the electric motor is restarted. More specifically, this may include restarting the electric motor when the phase of the electric power and the electric motor are substantially in phase, when the phase of the electric power is leading the phase of the electric motor, or at some other desired condition.
As will be described in more detail below, many of the benefits described may be enabled by increasing the amount of control over the electric power supplied to a load. For example, independently controlling each phase of three-phase power may enable detection of faults (e.g., a phase-to-ground short or a phase-to-phase short) while minimizing the duration, the peak current, and/or the let through energy of the faulty condition. Accordingly, it would be beneficial to utilize a switching device capable of increasing control over electric power supplied to the load, for example, by enabling each phase of electric power to be independently controlled.
Additionally, since switching device may be utilized in various implementations, such as a wye-delta starter, a reverser, a motor drive bypass, and so forth, it would be beneficial to utilize a switching device that can be modularly configured for various implementations, for example, to minimize footprint and/or interconnections (e.g., cabling) of the switching devices. More generally, modular arrangements, such as single-phase switching modules that can be incorporated alone or as a group, may enable a highly flexible modular design and manufacturing platform, which allows for assemblies of devices for many different needs and markets.
Moreover, while many of the foregoing improvements may be used together, they may also be used separately with significant potential for improvement in the field of switching and power systems. For example, single-phase switching devices may be used in POW (e.g., timed) application and/or conventional (e.g., non-timed) applications. Additionally, a motor control device (e.g., a wye-delta starter) may also be used in POW (e.g., timed) application and/or conventional (e.g., non-timed) applications. The present disclosure relates to various different technical improvements in the field, which may be used in various combinations to provide advances in the art.